Polycrystalline diamond element

ABSTRACT

An embodiment of a PCD insert comprises an embodiment of a PCD element joined to a cemented carbide substrate at an interface. The PCD element has internal diamond surfaces defining interstices between them. The PCD element further comprises a working surface and a low melting point region adjacent the working surface in which the interstices are at least partially filled with a low melting point metallic material having a melting point of less than about 1,300 degrees centigrade at atmospheric pressure, or less than about 1,200 degrees centigrade at atmospheric pressure. The PCD element includes an intermediate region, the interstices of the intermediate region being at least partially filled with a catalyst material for diamond.

FIELD

This invention relates to polycrystalline diamond (PCD) elements, particularly but not exclusively to PCD elements suitable for use in attack tools and cutters, such as picks and rotary drill bits, as may be used in the mining, tunneling, construction and oil and gas industries to process or degrade pavements, rock formations and the like, or to bore into the earth.

BACKGROUND

Cutter inserts for drill bits for use in boring into the earth may comprise a layer of polycrystalline diamond (PCD) bonded to a cemented carbide substrate. Such cutter inserts may be referred to as polycrystalline diamond compacts (PDC).

PCD is an example of a superhard, also called superabrasive, material comprising a mass of substantially inter-grown diamond grains, forming a skeletal mass defining interstices between the diamond grains. PCD material comprises at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa and temperature of at least about 1,200 degrees centigrade in the presence of a sintering aid.

Suitable sintering aids for PCD may also be referred to as a catalyst material for diamond. Catalyst material for diamond is understood to be material that is capable of promoting direct inter-growth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite. Some catalyst materials for diamond may promote the conversion of diamond to graphite at ambient pressure, particularly at elevated temperatures. Examples of catalyst materials for diamond are cobalt, iron, nickel and certain alloys including any of these. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. The interstices with PCD may at least partly be filled with a material, which may be referred to as a binder or a filler material. In particular the interstices may be wholly or partially filled with catalyst material for diamond.

Components comprising PCD are used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. For example, PCD bodies are commonly used as cutter inserts on drill bits used for boring into the earth in the oil and gas drilling industry. PCD bodies are also used for machining and milling metal-containing bodies, such as may be used in the auto manufacturing industry. In many of these applications the temperature of the PCD material becomes elevated as it engages a rock formation, workpiece or body with high energy.

PCD is extremely hard and abrasion resistant, which is the reason it is the preferred tool material in some of the most extreme machining and drilling conditions, and where high productivity is required. A disadvantage of PCD containing certain catalyst materials for diamond as a filler material may be its relatively poor thermal stability above about 400 degrees centigrade. The catalyst material may promote the degradation of the PCD at elevated temperature, particularly at temperatures greater than about 750 degrees centigrade, as may be experienced in manufacture and use of PCD compacts.

United States patent application publication number 2007/0079994 discloses thermally stable diamond-bonded compacts that include a diamond-bonded body comprising a thermally stable region that extends a distance below a diamond-bonded body surface. The thermally stable region has a material microstructure comprising a matrix first phase of bonded together diamond crystals, and a second phase interposed within the matrix first phase. The second phase comprises one or more reaction products formed between one or more infiltrate material and the diamond crystals at high pressure/high temperature (HPHT) conditions. The infiltrate or replacement material may include one or more of the following elements: Si, Cu, Sn, Zn, Ag, Au, Ti, Cd, Al, Mg, Ga, Ge, which may also be used in compounds containing conventional solvent-catalyst materials (transition metals) where the solvent catalyst is rendered inactive by reaction with another material.

United States patent application publication number 2008/0230280 discloses a PCD construction comprising a first region positioned remote from a surface and that includes a replacement material. The replacement material may be a noncatalyzing material that is disposed within interstitial regions between the diamond crystals in the first region. The noncatalyzing material can have a melting temperature of less than about 1,200 degrees centigrade and can be selected from low melting point metallic materials and/or alloys including elements, which can include those from Group IB of the Periodic table, such as copper. It is additionally desired that the replacement material display negligible or no solubility for carbon.

There is a need to provide a polycrystalline diamond (PCD) element having enhanced thermal stability.

SUMMARY

A purpose of the invention is to provide a (PCD) element having enhanced thermal stability.

A first aspect of the invention provides a polycrystalline diamond (PCD) element having internal diamond surfaces, the internal diamond surfaces defining interstices between them, the PCD element comprising a working surface, a low melting point region adjacent the working surface and in which the interstices are at least partially filled with a low melting point metallic material having a melting point of less than about 1,300 degrees centigrade at atmospheric pressure, or less than about 1,200 degrees centigrade at atmospheric pressure; and an intermediate region extending a distance of between about 5 microns and about 600 microns from a boundary defined by the low melting point region, the interstices of the intermediate region being at least partially filled with a catalyst material for diamond.

In one embodiment, the PCD element is bonded to a substrate at an interface and the intermediate region of the PCD element extends from the boundary defined by the low melting point region and the interface. In some embodiments, the intermediate region extends a distance from the boundary of at most about 400 microns, at most about 200 microns, at most about 100 microns, at most about 50 microns, at most about 10 microns or even at most about 5 microns. In some embodiments, the intermediate region extends a distance from the boundary of at least about 5 microns, at least about 10 microns, at least about 50 microns, at least about 100 microns, or even at least about 200 microns.

In one embodiment of the invention, the interstices of the intermediate region are at least 50% filled with a sintering aid or catalyst material for diamond, such as cobalt.

In some embodiments, the low melting point region extends a depth into the PCD element from the working surface, the depth being at most about 1,000 microns, at most about 500 microns or at most about 100 microns. In some embodiments, the low melting point region extends a depth into the PCD element from a working surface, the depth being at least about 5 microns, at least about 10 microns, at least about 50 microns, at least about 100 microns, or even at least about 200 microns.

In one embodiment, the low melting point region is in the form of a stratum or layer. In some embodiments, the low melting point region is in the form of a layer or stratum that extends to a depth of at least about 40 microns, at least about 100 microns or even at least about 200 microns from a working surface.

In one embodiment of the invention, the interstices within the low melting point region are at least 50 percent, at least about 70 percent, at least about 80 percent or at least about 90 percent filled with the low melting point metallic material.

In one embodiment of the invention, the low melting point metallic material has a melting point lower than 1,100 degrees centigrade at atmospheric pressure.

In some embodiments of the invention, the low melting point metallic material has a melting point greater than about 600 degrees centigrade or greater than about 700 degrees centigrade at atmospheric pressure.

Embodiments of the invention have the advantage that the low melting point metallic material does not substantially melt when the PCD element, is brazed onto a tool carrier at temperatures of several hundred degrees centigrade.

In one embodiment of the invention, the low melting point metallic material is not capable of reacting to form a stable carbide at less than about 1,000 degrees centigrade at atmospheric pressure.

Embodiments of the invention have the advantage that the low melting point metallic material does not react with the diamond to form carbides. The formation of carbide grains may retard the rate of infiltration of the low melting point metallic material in manufacture and may create undesirable stresses within the interstices due to volume changes occurring with the formation of new phases and compounds. The formation of carbides as a reaction product of a reaction between the low melting point metallic material and the diamond of the PCD would necessarily require some of the surrounding diamond to be sacrificed to the reaction, which may compromise the integrity of the microstructure.

In some embodiments of the invention, the low melting point metallic material is Ag, Mg, Cu or Pb in elemental form or an alloy including any of these elements, and in some embodiments the low melting point metallic material is Ag or Cu in elemental form or an alloy including either of these elements. In one embodiment, the low melting point metallic material has the characteristic that it is substantially resistant to oxidation.

Embodiments of the invention have the advantage of having enhanced thermal stability without substantially compromising strength.

In one embodiment of the invention, the PCD element is bonded at an interface to a cemented carbide substrate, such as a cobalt-cemented tungsten carbide substrate, and in one embodiment, the PCD element is bonded to a hard-metal substrate via a bonding layer having a coefficient of thermal expansion intermediate that of the PCD and the hard-metal. In one embodiment, the bonding layer comprises diamond grains and metal carbide, wherein the diamond grains are not substantially bonded to each other. In one embodiment, the PCD element comprises an intermediate region that is remote from the working surface, in which the interstices are at least 50% filled with a catalyst material for diamond, the intermediate region being adjacent the interface and the low melting point region is remote from the interface.

A second aspect of the invention provides an insert for a tool, the insert comprising an embodiment of a PCD element according to the invention.

A third aspect of the invention provides a tool comprising an embodiment of an insert according to the invention.

In some embodiments, the tool is suitable for machining, drilling, boring, cutting or otherwise forming or degrading a hard or abrasive workpiece or other body, such as rock, concrete, asphalt, metal or hard composite materials. In some embodiments, the tool is a drill bit for use in earth boring, rock drilling or rock degradation, as may be used in the oil and gas drilling and mining industries, and in one embodiment, the tool is a rotary drag bit for use in earth-boring and rock drilling in the oil and gas industry.

A fourth aspect of the invention provides a method for making a PCD element, the method including providing a PCD body comprising a sintering aid within interstices of the PCD body, removing at least some of the sintering aid from a portion of the polycrystalline diamond element to form a porous region adjacent a working surface, and infiltrating or permeating at least a portion of the porous region with low melting point metallic material having a melting point of less than about 1,300 degrees centigrade at atmospheric pressure, or less than about 1,200 degrees centigrade at atmospheric pressure.

In one embodiment, substantially all of the sintering aid is removed from the PCD element.

One embodiment of the method of the invention includes preventing or avoiding filling the pores within a part of the porous region with the low melting point metallic material.

One embodiment of the method of the invention includes infiltrating a material comprising a catalyst material for diamond, such as cobalt, into a part of the porous region not filled with the low melting point metallic material.

In one embodiment of the invention, a controlled temperature cycle is employed in such a manner as to allow sufficient or a certain amount of the low melting point metallic material to be introduced into the porous region prior to infiltration with the material comprising a catalyst material for diamond.

DRAWING CAPTIONS

Non-limiting embodiments will now be described with reference to the drawings, of which

FIG. 1 shows a schematic longitudinal cross sectional view of an embodiment of a PCD element.

FIG. 2 shows a schematic expanded cross sectional view of a region of the embodiment shown in FIG. 1.

FIG. 3A shows schematic perspective views of components used in an embodiment of a method for manufacturing PCD compacts or inserts.

FIG. 3B shows a schematic perspective view of an embodiment of a PCD compact or insert.

The same references in all drawings refer to the same features, unless otherwise indicated.

DETAILED DESCRIPTION OF EMBODIMENTS

As used herein, a “working surface” of an insert or element is any part of the insert or element which may in use contact a workpiece or body being worked. It is understood that any portion of a working surface is also a working surface.

As used herein, the term “low melting point metallic material” means metal in elemental or alloy form, which possesses the characteristic properties of a metal, including high electrical conductivity, thermal conductivity and fracture toughness. The term excludes compounds of metals, such as metal carbides, oxides, nitrides, carbo-nitrides, and other ceramics or inter-low melting point metallic materials that do not possess metallic properties.

As used herein, a catalyst material for diamond is a material that is capable of promoting the precipitation, growth and/or sintering-together of grains of diamond under a condition of pressure and temperature at which diamond is more thermodynamically stable than graphite. Examples of catalyst materials for diamond are iron, nickel, cobalt, manganese and certain alloys including any of these elements. Some catalyst materials for diamond are capable of promoting the conversion of diamond into graphite at ambient pressure, particularly at elevated temperatures.

With reference to FIG. 1 and FIG. 2, an embodiment of a PCD insert 200 comprises an embodiment of a PCD element 100 joined to a cemented carbide substrate 220 at an interface 116. The embodiment of the PCD element 100 has internal diamond surfaces 102, the internal diamond surfaces 102 defining interstices 104 between them. The PCD element 100 further comprises a working surface 114 and a low melting point region 111 adjacent the working surface 114 and in which the interstices 104 are at least partially filled with a low melting point metallic material having a melting point of less than about 1,300 degrees centigrade at atmospheric pressure, or less than about 1,200 degrees centigrade at atmospheric pressure. An intermediate region 112 extends a distance of between about 5 microns and about 600 microns from a boundary 116, the interstices 104 of the intermediate region 112 being at least partially filled with a catalyst material for diamond. In this embodiment, the boundary is the interface (both indicated by reference number 116).

The person skilled in the art will appreciate that PCD inserts of a wide range of shapes and sizes can be made, depending on the type of application. The inserts are particularly advantageous when used in applications where the insert may be subjected to high temperatures, and therefore where high thermal stability is important. An especially favoured application is as inserts for rotary drill bits used for rock drilling and earth boring in the oil and gas industry.

With reference to FIG. 3A, an embodiment of a method for making a PCD element includes providing a PCD insert 300 that has been manufactured using an ultra-high pressure and high temperature (HPHT) method well-known in the art. The insert 300 comprises a PCD element 310 integrally bonded to a cemented carbide hard-metal substrate 320. The microscopic interstices (not shown) of the PCD element 310 are substantially filled with cobalt catalyst material. At least a part of PCD element 310 is detached from the insert 300 to produce a PCD body 311. One way of detaching the PCD element 310 is to grind away the substrate 320. The PCD body 311 is treated to remove catalyst material from the interstices to produce a porous and thermally stable PCD element 312. The porous PCD element 312 is then contacted on one side with a second cemented carbide substrate 340 and on the opposite side with a source 330 of low melting point metallic material. The source 330 may be in the form of a thin foil or disc, or powder. The substrate 340 includes tungsten carbide grains and a cobalt metal binder, the metal binder being capable of acting as a catalyst material to promote the growth and sintering of diamond grains. The porous PCD element 312, thus “sandwiched” between the substrate 340 and the foil or disc 330 is treated at an ultra-high pressure in excess of about 5 GPa at temperatures sufficiently high to melt the low melting point metallic material and to melt the cobalt metal binder of the substrate 340, resulting in some of it infiltrating into the porous PCD element 312. The temperature cycle may be controlled in such a manner as to allow sufficient or a certain amount of the low melting point metallic material to be introduced into the porous PCD element 312 prior to the cobalt metal binder material melting and infiltrating into the porous PCD element 312. After this treatment, the resulting insert is removed and processed to final dimensions and tolerances to produce an embodiment of a finished PCD insert 200 shown in FIG. 3B, comprising a PCD element 100 joined to a cemented carbide substrate 220.

In one embodiment, the PCD body has a thickness between a pair of opposite surfaces of at least about 1.5 mm or at least about 1.8 mm, one of the pair contacted with a source of low melting point metallic material and the other of the pair contacted with a source of catalyst material for diamond.

One embodiment of the method of the invention includes heating a source of low melting point metallic material to a temperature within the range between the melting point of the low melting point metallic material and the melting point of the catalyst material, maintaining the temperature within this range for a period of time sufficient for the infiltration or permeation of the low melting point metallic material to be completed. In one embodiment, the temperature is then increased to greater than the melting point of the catalyst material for a period of time for the introduction of the catalyst material to be completed.

One embodiment of the method includes contacting one surface of a porous PCD body with a source of silver, contacting another surface of the PCD body with a source of cobalt to form an assembly, subjecting the assembly to a pressure of at least about 5.5 GPa, heating the assembly to a temperature in the range above the melting point of silver at the pressure and below the melting point of cobalt at the pressure, maintaining temperature within this range for a period of time of at least about 2 minutes or at least about 3 minutes, and then increasing the temperature to above the melting point of cobalt at the pressure.

One embodiment of the method includes contacting one surface of a porous PCD body with a source of copper, contacting another surface of the PCD body with a source of cobalt to form an assembly, subjecting the assembly to a pressure of at least about 5.5 GPa, heating the assembly to a temperature in the range above the melting point of copper at the pressure and below the melting point of cobalt at the pressure, maintaining temperature within this range for a period of time of at least about 1 minute or at least about 2 minutes, and then increasing the temperature to above the melting point of cobalt at the pressure.

In some embodiments, the period of time is at most about 15 minutes or even at most about 10 minutes.

The sintered PCD body can be produced in an ultra-high pressure furnace by sintering together diamond grains in the presence of a catalyst material for diamond at a pressure of at least about 5.5 GPa and a temperature of at least about 1,300 degrees centigrade. The catalyst material may comprise a conventional transition metal type diamond catalyst material, such as cobalt, iron or nickel, or certain alloys thereof. The sintered PCD body, as a whole or at least a region thereof, may then be rendered thermally stable, for example, through the removal of the majority of binder catalyst material from the PCD body or desired region using acid leaching or another similar process known in the art.

The catalyst material present in the PCD body 311 may be removed by any of various methods known in the art, such as electrolytic etching, evaporation techniques, acid leaching (for example by immersion in a liquor containing hydrofluoric acid, nitric acid or mixtures thereof) or by means of chlorine gas, as disclosed in international patent publication number WO2007/042920, or by another method (e.g. as disclosed in South African patent number 2006/00378).

In one embodiment of the method, a PCD insert similar to PCD insert 300 in FIG. 3A, is provided. A region adjacent the working surface of the PCD element is depleted substantially of catalyst material by means of method known in the art, resulting in the region being porous. A low melting point metallic material is introduced into the pores of the porous region. The parameters of the method of introduction may be controlled to retain porosity within part of the porous region. A catalyst material is then infiltrated into the remaining pores of the masked or passivated region. This may be done by contacting a source of catalyst material with the working surface of the PCD element, assembling the PCD insert and the source into a capsule of a kind used for HPHT sintering of PCD, and subjecting the assembly to an ultra-high pressure and temperature at which the catalyst material is molten and the diamond is thermodynamically more stable than graphite. In some embodiment, the pressure is at least about 5.5 GPa, at least about 6 GPa or at least about 6.5 GPa. In one embodiment, the pressure is about 6.8 GPa.

The low melting point metallic materials according to the invention are substantially inert with respect to diamond and do not substantially promote its dissolution or degradation at ambient pressures. They may function as a heat conducting filler within the PCD element. While wishing not to be bound by any particular hypothesis, low melting point metallic materials are believed not to degrade diamond at the high temperatures that may be experienced in use, i.e. up to about 1,100 degrees centigrade. At temperatures for which the low melting point metallic material is in the solid phase, its presence in the interstices may enhance the strength of the PCD. In addition, the high thermal conductivity of the low melting point metallic material may further enhance the thermal stability of the polycrystalline diamond element in comparison to leached PCD. At temperatures for which the low melting point metallic material is in or close to the molten phase, stress may be prevented from building up within the PCD by virtue of the low melting point metallic material leaking from the interstices as it thermally expands or melts. Solid metals close to their melting points generally have greatly reduced yield strength, which reduces build up of micro-stresses that may arise from a mismatch in the thermal expansion coefficients. Melting or softening of the metal may have the additional benefit of lubricating the action of the polycrystalline diamond element at high temperatures. The low melting point of the low melting point metallic material means that relatively low temperatures are required to infiltrate it into a polycrystalline diamond element in manufacture. In some embodiments of the method of the invention, the rate and extent of infiltration may readily be controlled by controlling its viscosity by controlling the temperature, without need to use very high temperatures.

EXAMPLES

The invention will now be described, by way of example only, with reference to the following non-limiting examples.

Example 1

A PCD insert having a diameter of about 16 mm and for use in a rotary drag bit for oil and gas drilling was used as the starting component. The insert was substantially cylindrical in form and comprised a PCD layer integrally bonded to a Co-cemented WC hard-metal substrate. The PCD layer was about 2.3 mm thick and the diamond grain size distribution was of a multi-modal type, comprising sintered diamond grains with average grain size of less than about 20 microns, the interstices between the diamond grains being filled with Co, a catalyst metal sourced from the hard-metal substrate during the step of sintering the PCD. Substantially all of the hard-metal substrate was machined away from the PCD layer, providing a PCD disc. Substantially all the Co was then removed from the PCD disc by immersing it in a mixture of hydrofluoric and nitric acid for several days, resulting in a porous, detached PCD disc. The PCD disc was heat treated in vacuum in order to remove (i.e. “outgas”) any residual organic impurities that may be present.

The porous PCD disc was then re-infiltrated with cobalt from one side and copper from an opposite side, and simultaneously re-bonded to a second Co-cemented WC substrate. This re-infiltration step was carried out at an ultra-high pressure of greater than about 5 GPa, at which diamond is thermodynamically stable, and a temperature of about 1,400 degrees centigrade at which Co is molten at the ultra-high pressure. In order to carry out this step, a pre-form assembly was prepared, the pre-form assembly comprising the porous PCD disc placed onto a flat surface of a cylindrical substrate, and a thin film of copper placed on top of the porous PCD disc. The copper film was less than 0.5 mm thick and had been ultrasonically cleaned in an acetone bath.

The assembly comprising the PCD disc thus “sandwiched” between the copper foil and the substrate was placed within a refractory metal jacket, which was subsequently placed within a ceramic support and subsequently sealed within another metal casing, as is well known in the art. The pre-form assembly was assembled into a capsule for an ultra-high pressure furnace and subjected to the ultra-high pressure and temperature. The temperature was increased from ambient to the maximum level over a period of time once the target pressure had been achieved.

After the re-infiltration step, the insert was removed from the ultra-high pressure apparatus and the casing and jacketing was removed. The insert was then sliced into two parts along an axial plane, producing two cross-sectional surfaces. One of these surfaces was polished and analysed by means of SEM (scanning electron microscopy), revealing that the PCD had bonded well with the substrate and that substantially all of the interstices within the PCD were filled with copper, cobalt, or a combination of copper and cobalt. The copper had infiltrated from the flat working surface to a depth of about 1.7 mm, a region with a depth of about 1.3 mm from the flat working surface being substantially free of cobalt. The PCD interstices within about 0.2 mm from the substrate were filled principally with cobalt, although some copper was evident.

A second test insert was made as above and subjected to a wear test, which involved using the insert, suitably prepared as would be appreciated by the skilled person, to machine a granite block mounted on a vertical turret milling apparatus. The PCD layer displayed excellent wear resistance and thermal stability.

Example 2

A re-infiltrated insert was made using the same process as in Example 1, the only difference being that a silver foil was used instead of a copper foil. The insert was also analysed and tested as in Example 1.

The silver had infiltrated more deeply into the PCD than had the copper, to a depth of about 2.2 mm from the flat working surface. This is believed to be due to the lower melting point of silver and consequently the fact that it would have melted at an earlier stage than the copper, therefore having more time to infiltrate the porous PCD before the cobalt melted and began infiltrating from the opposing direction.

Example 3

A porous PCD disc can be prepared using the process described in Example 2, and the silver can be introduced into the pores prior to the treatment at ultra-high pressure. This can be done by placing the porous PCD disc into a graphite vessel, and disposing a silver film on top of it, the silver film having been ultra-sonically cleaned in an acetone bath. The vessel can then be placed in a furnace and its contents heated in a vacuum to above the melting point of the silver, i.e. to about 1,000 degrees centigrade, causing the silver foil to melt and infiltrate the PCD disc.

Example 4

A porous PCD disc can be prepared using the process described in Example 2 and silver can be introduced into the pores prior to the treatment at ultra-high pressure by depositing a very thin film of silver onto a flat surface of the PCD disc by means of sputtering and then causing it to melt. The mass of the silver deposited can be calculated to be just sufficient for 10% of the pores to be filled with silver, and consequently to provide just enough silver to infiltrate the PCD to a depth of about 10% of its thickness, i.e. to a depth of about 230 microns from the flat surface, leaving the remaining pores substantially empty. This mass could be about 12.5 milligrams. The film thickness should be as uniform as possible across the PCD surface.

The silver-coated PCD can then be placed into a graphite vessel, with the coated surface remote from the base of the graphite vessel (i.e. on the top surface), and the vessel placed into a furnace. The vessel and its contents can be heated in a vacuum to above the melting point of the silver, i.e. to about 1,000 degrees centigrade, causing the silver coating to melt and infiltrate the PCD disc.

Example 5

A free-standing fully leached PCD disc was produced according to a similar process to that disclosed in Example 1. Diamond powder having a size distribution that can be resolved into at least two distinct peaks was placed against a cobalt cemented tungsten carbide substrate, and this assembly was encapsulated in a refractory metal jacket and subjected to an ultra-high pressure of at least about 5.5 GPa and a temperature of at least about 1,500 degrees centigrade to sinter the diamond powder into a PCD layer bonded to the substrate. After sintering the PCD disc was separated from the substrate by lapping away the carbide base and substantially all of the cobalt was removed from the interstices of the PCD by means of leaching in an acid liquor, as is well known in the art, to form a porous PCD body having a generally disc form.

A copper disc was placed against one end of the porous PCD body and a cobalt cemented tungsten carbide substrate was placed against the opposite end of the PCD body, and this assembly was encapsulated within a refractory metal jacket. The porous PCD body was thus sandwiched between the substrate and the copper disc. The copper disc had a thickness of about 0.25 mm and diameter substantially the same as that of the PCD body. The mass of the copper discs was at around 420 mg, which equates to less than about 10 percent of the volume of the PCD body, and was at a level considered to be in excess of the volume required to fill the entire void created during the leaching process.

The assembly was further encased in a manner known in the art for HPHT sintering and subjected to a second high pressure thermal cycle at a temperature of around 1,410 degrees centigrade and a pressure of around 5.2 GPa. The PCD insert comprising a PCD layer containing copper and cobalt, and joined to the substrate was recovered and machined to final specifications to form a PCD cutter insert.

The PDC cutter insert was subjected to a milling test, which involved a high-rotational speed cutting of a granite work piece and is considered to be a very thermally aggressive test. The results suggest a dramatic improvement in thermal stability above that of a control PCD cutter insert, which had not undergone the process of re-infiltration of copper.

Example 6

A further material was made using the method disclosed in Example 5, but by substituting the copper disc with 520 mg of silver powder. Once again, the mass was chosen to correspond to around 10 vol % of the fully leached disc. The conditions selected for the second high pressure thermal cycle were identical to those used in Example 5. Performance results from this material showed an improvement in thermal stability above that of non-reinfiltrated PCD. 

1. A polycrystalline diamond (PCD) element having internal diamond surfaces, the internal diamond surfaces defining interstices between them, the PCD element comprising a working surface, a low melting point region adjacent the working surface and in which the interstices are at least partially filled with a low melting point metallic material having a melting point of less than about 1,300 degrees centigrade at atmospheric pressure, and an intermediate region extending a distance of between about 5 microns and about 600 microns from a boundary defined by the low melting point region, the interstices of the intermediate region being at least partially filled with a catalyst material for diamond.
 2. A polycrystalline diamond element according to claim 1, in which the intermediate region extends a distance from the boundary of at most about 400 microns.
 3. A polycrystalline diamond element according to claim 1, in which the intermediate region extends a distance from the boundary of at least about 5 microns.
 4. A polycrystalline diamond element according to claim 1, in which the interstices of the intermediate region are at least 50% filled with a sintering aid or catalyst material for diamond.
 5. A polycrystalline diamond element according to claim 1, in which the low melting point region extends a depth into the PCD element from the working surface, the depth being at most about 1,000 microns.
 6. A polycrystalline diamond element according to claim 1, in which the low melting point region extends a depth into the PCD element from the working surface, the depth being at least about 5 microns.
 7. A polycrystalline diamond element according to claim 1, in which the low melting point region is in the form of a stratum or layer.
 8. A polycrystalline diamond element according to claim 1, in which the interstices within the low melting point region are at least 50% filled with the low melting point metallic material.
 9. A polycrystalline diamond element according to claim 1, in which the low melting point metallic material has a melting point lower than 1,100 degrees centigrade at atmospheric pressure.
 10. A polycrystalline diamond element according to claim 1, in which the low melting point metallic material has a melting point greater than 600 degrees centigrade at atmospheric pressure.
 11. A polycrystalline diamond element according to claim 1, in which the low melting point metallic material is not capable of reacting to form a stable carbide at less than 1,000 degrees centigrade at atmospheric pressure.
 12. A polycrystalline diamond element according to claim 1, in which the low melting point metallic material is Ag, Mg, Cu or Pb in elemental form or an alloy including any of these elements.
 13. A polycrystalline diamond element according to claim 1, in which the low melting point metallic material is Ag or Cu in elemental form or an alloy including either of these elements.
 14. An insert for a tool, the insert comprising a polycrystalline diamond element according to claim
 1. 15. A tool comprising an insert according to claim
 14. 16. A method for making a polycrystalline diamond (PCD) element, the method including providing a PCD body comprising a sintering aid within interstices of the PCD body, removing at least some of the sintering aid from a portion of the polycrystalline diamond element to form a porous region adjacent a working surface, and infiltrating or permeating at least a portion of the porous region with low melting point metallic material having a low melting point of less than 1,300 degrees centigrade at atmospheric pressure.
 17. A method according to claim 16, in which substantially all of the sintering aid is removed from the polycrystalline diamond element. 